How can i change a curve to have the same proportions on all its vertices?
First, select the good vertices in edit mode (at least three, one whole waveform):



Then press Shift+D, and then P to separate the new vertices into a new curve:



Now add an Array modifier to the new curve, making sure to tick the Merge checkbox:



You should now have something like this:



Notice that the fewer waveforms you select initially the more accurate the result will be, although it will take vastly more repeats on the Array modifier. It is however completely adjustable at that point, so it can be given the exact same number of waveforms as your other curve.

Once you are happy with the result, change the handles to vector, press Alt+C and convert to mesh, then the same and convert back to a curve, and change the handle type back to whatever it was. You should now have one continuous curve. The reason you need to do this is because you are not allowed to apply a constructive modifier on a curve.